This application is related to Japanese Patent Application No. 2000-367052 filed on Dec. 1, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a hot-water supply system in which water is boiled using electrical power.
2. Description of Related Art
In a conventional hot-water supply system described in JP-B2-2858788 or in JP-B2-63-35904, electrical power is supplied to a heater in a midnight time zone which is cheapest in power rate, so that water is boiled and a hot-water storage tank is filled up in the midnight time zone. Specifically, in the conventional system of JP-B2-2858788, an on-off control of an electrical supply to the heater core is performed at different time zones. On the other hand, in the conventional system of JP-B2-63-35904, the supply of the electrical power to the heater starts from a start time of the midnight time zone.
However, in the-above-described conventional systems, because a hot-water amount to be stored in the tank is limited, the hot-water amount stored in the midnight time zone becomes insufficient in a home using hot water more than the the hot-water amount stored in the tank in a time zone from the morning to the midnight (e.g., 7:00 to 23:00). Accordingly, in the time zone of evening or night, hot water may become short. In this case, when the water is boiled in a time zone except for the midnight time zone, the power rate is increased.
In a home where a small-amount of hot water is used in the time zone from the morning to the midnight (e.g., 7:00 to 23:00) and a large amount of hot water is stayed in the tank at the time of 23:00, the heat radiation of hot water in an unused time period is caused. On the other hand, in a home where a large-amount of hot water is used in one day, a shortage of hot water may be caused.
In view of the foregoing problems, it is an object of the present invention to provide a hot-water supply system which restricts a wasteful heat radiation of hot water stored in a tank while preventing a shortage of hot water.
According to the present invention, a hot-water supply system includes a tank for storing hot water for a supply, a water-heating unit operated electrically for heating water by performing boiling operation, and a control unit for controlling the boiling operation of the water-heating unit. The control unit includes use heat-quantity calculating means for calculating a heat quantity used in a predetermined time period based on a hot-water supply amount from the tank in the predetermined time period and for learning the heat quantity used in the predetermined time period, target heat-quantity calculating means for calculating a target heat quantity for boiling based on the learned heat quantity in the use heat-quantity calculating means, target temperature calculating means for calculating a target boiling temperature of water based on the target heat quantity calculated by the target heat-quantity calculating means, and boiling means for performing boiling operation of the water-heating unit by a necessary boiling amount based on the target boiling temperature calculated from the target temperature calculating means. In the hot-water supply system, the boiling operation is performed by the necessary boiling amount, it can prevent a wasteful heat radiation of hot water stored in the tank while preventing a shortage of hot water.
Preferably, the control unit further includes time-zone heat-quantity calculating means for calculating and learning a heat quantity used in each time zone based on each hot-water supply amount during a plurality of time zones in which power rate are different from each other, present heat-quantity calculating means for calculating a heat quantity stored in hot water within the tank at the present time, shortage estimating means for estimating a shortage of the heat quantity stored in hot water within the tank based on the heat quantity from the time-zone heat quantity calculating means and the heat quantity from the present heat quantity calculating means, and compulsory-boiling means for additionally performing the boiling operation in accordance with a shortage amount of the heat quantity when the shortage is estimated by the shortage estimating means. Accordingly, a shortage of hot water in each time zone can be prevented.
Preferably, the control unit includes hot-water amount detecting means for detecting a hot-water amount stored in the tank. Further, as the hot-water amount stored in the tank at a start time of the midnight time zone is smaller, the first boiling time period is set longer and the first boiling start time is set earlier. Therefore, the boiling operation can be accurately finished before the finish of the midnight time zone. Accordingly, heat loss in the midnight time zone can be prevented.